Broken

Broken (or busted) is a subjective term referring to any card or strategy that gives it user an extraordinary advantage over that of the enemy player, that can define the competitive metagame in a somewhat imbalanced manner, leading to both eventual ire, and for many players to use it. Godvault: Secrets of Outhria has been known for many broken cards over the years which ultimately thanks to user critique, gets phased out of Championship mode, but nevertheless is playable in Standard and Wild.

Examples of broken cards

 * Ancieus Uredos, for 8 mana you could get a minion with Rush, Taunt, and Barrier for 12 damage and 16 health. On top of this, he also equipped a custom Eldjorn weapon of the player's choice (sword, bow, staff) that had 5 damage and 3 durability. Essentially, you're getting a 13 mana card. Ancieus' cost was later changed to 9, and players are still speculative of it having Barrier which still makes it one of the most viable 9-drops in the game.
 * Tylious Dawnbane is considered to be one of the most broken cards in the game, despite costing 9-mana, and requiring the Endgame phase to summon it. He freezes the enemy hero as a Battlecry, which means they take more damage from any spells the player has at their disposal. In addition, Tylious can kill a minion off the bat, activating his Enrage, gaining +3 Attack, and then activating one of his effects which provides the player with an absurd amount of choice. They can either Poison a minion for 1 (which leads to an eventual 6 damage), heal Tylious for 3, or gain a Paradox Gem. Because of this, players gain a ridiculous advantage when he is summoned, often leading to winning the game.
 * Deathlius Loss'end is considered to be one of the most broken finisher cards in the game, since his damage stat matches his health stat whenever he fights a character; a character, not a minion. Because he possesses Ironwilled in which he takes no damage battling minions when he attacks, Deathlius can clear any minion on the board with almost no problem. His Enrage, where he makes all of his damage do Overkill is also considered broken as well. It is common to see players inflict a point of damage on him before sending him to destroy a weak minion, essentially dealing ludicrous amounts of Overkill damage. On top of that, what makes Deathlius highly "busted", is that despite the enemy lowering his attack at any time, if Deathlius and the enemy hero have the same health, or the hero has any less than Deathlius' health, Deathlius one shots the hero due to his ability. It is a common play to see Deathlius played, extremely buffed (let's say the use of two Rising Spirit) and attack the enemy hero, resulting in an OTK.
 * Kagamoni is often considered to be one of the most busted cards there is, due to the fact it can copy any minion, even your opponents, and gains their effects until it dies at the end of the turn. Its only drawback is minions with Defiant, but it can still be a threat having the power to mimic almost anything.
 * Tanin Starkfaust is considered to be one of the best 7-drop minions in the game, dealing 2-5 damage to ALL minions, essentially by chance destroying any minion that costs 3 or less (and sometimes 4) and then giving a weapon to both players that can change the game. On top of this, Tanin has Taunt, and if he had destroyed all enemy minions, your opponent will have to play a lot to remove him.